Listeria monocytogenes (Lm) is a gram-positive, food-borne facultative intracellular bacterial pathogen that infects humans and causes disease following bacterial translocation across the intestinal barrier. While healthy individuals usually exhibit mild forms of disease such as gastroenteritis, individuals who are immune-compromised as well as elderly patients often suffer more severe forms of illness that include meningoencephalitis and septicemia. A significant but much less well-documented sequelae of invasive Lm infections involve the heart; this type of infection is estimated to occur in at least % to 10% of those with invasive disease. Recently published data indicates that significant subpopulations of Lm strains have the capacity to target and invade cardiac cells; this is a new finding with important clinical implications. Experiments outlined within this proposal will test te hypothesize that cardioinvasive Lm strains have developed novel mechanisms and/or express novel or altered bacterial factors that enable them to replicate within cardiac tissues. These studies will provide a detailed understanding of the pathogenesis and maturation of myocarditis resulting from Lm infection, and will clarify bacterial factors that contribute to specific host tisue tropisms. Aim 1 will decipher the pathology of Lm cardioinvasive strains in animal infection models. Bacterial infections will be monitored in mice using in vivo bioluminescence imagining to determine the progression of cardiac infection as well as the potential for bacterial colonization at other body sites. Experiments will also include the histological examination of target tissues to characterize sites of host immune cell infiltration as well as the use of immuno-spin capture technology to definitively identify cellular damage that occurs as a result of the hos inflammatory response to Lm infection. Aim 2 will focus on the functional characterization of bacterial factors associated with invasive cardiac infections. Genetic and cellular approaches will be used to identify Lm factors that enhance cardiac invasion relative to the invasion of other cell types. The ultimate goal of these studies will be to establish and functionally characterize a cardiac model of infection for Lm and to determine the bacterial factors that contribute to the enhanced ability of selected Lm strains to invade and destroy cardiac tissue. This information will be useful for the early identification of Lm outbreak strains that pose increased risk for patient heart infections. Finally, the experiments outlined in this proposal will provide important insight into the mechanisms that establish bacterial tropism for specific host tissues and in addition will identify in vivo cellular targets of oxidative damage resulting from host inflammator responses to infection.